This invention relates to a drive system used to rotate a take-up reel on a component feeder. In particular, this invention is manifested in an articulated pawl used to drive teeth on a take-up reel.
Surface mount technology is widely used in the electronics industry today. The need to put ever more components on smaller and smaller circuit boards has driven the industry to develop smaller components and to place them closer together. Many of the electronic components today are too small to be easily handled and placed by hand.
The electronics industry has developed many new machines to handle and place these small components. One such device is a pick-and-place machine. This machine is a robotic device that picks up a component, generally by suction, and places it with great precision at a desired location on a printed circuit board. The components are fed into the pick-and-place machine by a peripheral mechanism known as a feeder.
Components are loaded on the feeder a variety of ways, including on tape-and-reel. In the tape and reel system, components are held inside a tape sandwich. The lower part of the tape typically is composed of pockets, and components are placed in the pockets to isolate the components from each other. A cover layer of tape is applied over the pockets, thereby trapping the components inside the pockets. The tape sandwich, containing the components, is many feet long and is wound around a reel and looks like a lumpy roll of masking tape.
This reel of tape and components is loaded onto the feeder and the feeder strips the top layer of tape off, thereby exposing a component. A pick and place machine picks up the exposed component and places it onto a printed circuit board. The feeder continues to feed components in this manner to the pick-and-place machine as required.
FIG. 1 shows a simplified tape and reel feeder. A reel of tape 102 is unrolled along a support 106. The tape 104 is guided by the support 106 to the initial roller/guide 108. The top layer 110 is stripped off of the tape 104 and wound around a take-up reel 112 by the rotation of the reel 112. After the top layer 110 is removed, a component 114 is exposed on the bottom layer 116 of the tape 104. The take-up reel 112 normally has teeth around the periphery and is driven by a pawl (not shown).
The Fuji IP1 is a typical pick and place machine which uses typical tape and reel feeders used by the electronics industry and operates essentially as shown in FIG. 1. FIG. 2 shows part of the drive system for the Fuji tape take-up reel. The take-up reel 202 has saw-tooth-shaped teeth 204 around the periphery. A spring-loaded drive pawl 206 is mounted on a vertical arm 208, which is connected by a spring 210 to a horizontal reciprocating arm 212. A vertical drive bar 214 is in sliding engagement with the horizontal arm 212.
In a retracted position, as shown in FIG. 2, the pawl 206 is held in the most rearward position by the vertical arm 208. The vertical arm 208 is moved into the rearward position by the movement of the reciprocating arm 212 and the drive bar 214. A pneumatic actuator (not shown) drives the vertical drive bar 214 rearward (pawl retracted) and forward (pawl advanced).
As the pawl 206 is retracted from a forward position, it slides over the back side 216 of the saw tooth shaped teeth 204 until the most rearward position is reached. A friction brake (not shown) prevents the take-up reel from moving during the retraction of the pawl 206.
To drive the take-up reel 202, the drive arm 214 is pulled forward, thereby forcing the reciprocating arm 212 forward. As the arm 212 is forced forward, the vertical arm 208 is pulled forward by a spring 210. The forward movement of the arm 208 forces the front edge 218 of the pawl 206 into engagement with the front edge 220 of the tooth 222. As the vertical arm 208 moves forward, the pawl 206 forces the tooth 222 forward, thereby rotating the take-up reel 202.
FIG. 3 shows the pawl 206, arms 208 and 212, and the drive bar 214 in a forward position. The cycle of forward and rearward movement of the drive bar 214 is continued as each new component is presented to the pick and place machine.
The prior art take-up reel system suffers from two main deficiencies. The first deficiency occurs during the retract phase of the drive cycle. The pawl does not always skip the same number of teeth and a difference of up to two teeth between successive retract cycles is common. This is a result of the tip of the pawl coming to rest on the tip of a tooth of the take-up reel, causing the pawl to "bounce" over a tooth rather than coming to rest between teeth as shown in FIG. 4. Because the pawl does not skip the same number of teeth on each retract cycle, the amount of top layer tape stripped off is indeterminate and may not be enough to expose a component fully on the bottom layer of the tape sandwich. If the top layer of tape is not stripped off the component, the pick-and-place machine will misfeed and require operator intervention.
The second deficiency is also manifested during the retraction of the pawl. At the end of some retract cycles, the pawl tip is supported on the top of a tooth, as shown in FIG. 5. As the pawl is driven forward, it does not engage the teeth properly, if at all. While the pawl is spring-loaded such that the tip of the pawl is forced down and into contact with the teeth, the force is insufficient to prevent missed teeth when the pawl is advanced at high speed. The spring force cannot be increased significantly, otherwise as the pawl will not slide over the back side of the teeth on the retract cycle and the reel will be rotated backwards. Hence, the pawl skips teeth during the forward drive cycle.
Because of the unreliability of the pawl design, misfeeds of the pick-and-place machine are common. Every misfeed requires an operator to manually intervene so production can continue. This intervention is inconvenient and expensive. Since a company that uses pick-and-place machines typically has a large number of the feeders, a major redesign, or replacement, of the feeders to fix the pawl misfeed problem would be expensive for the company.
With the above in mind, there exists a need in the electronics industry for a low cost and reliable take-up reel drive mechanism which can be retrofitted onto existing equipment.